The field of the invention relates to electro-optical readers or scanning systems, such as bar code symbol readers, and more particularly to the optical path design in a scanning module for use in applications requiring particularly compact bar code readers.
Electro-optical readers, such as bar code symbol readers, are now very common. Typically, a bar code symbol comprises one or more rows of light and dark regions, typically in the form of rectangles. The widths of the dark regions, i.e., the bars and/or the widths of the light regions, i.e., the spaces, between the bars encode information in the symbol.
A bar code symbol reader illuminates the symbol and senses light reflected from the regions of differing light reflectivity to detect the relative widths and spacings of the regions and derive the encoded information. Bar code reading type data input systems improve the efficiency and accuracy of data input for a wide variety of applications. The ease of data input in such systems facilitates more frequent and detailed data input, for example, to provide efficient inventories, tracking of work in progress, etc. To achieve these advantages, however, users or employees must be willing to consistently use the readers. The readers therefore must be easy and convenient to operate.
A variety of scanning systems is known. One particularly advantageous type of reader is an optical scanner which scans a beam of light, such as a laser beam, across the symbols. Laser scanner systems and components of the type exemplified by U.S. Pat. No. 4,387,297 and No. 4,760,248 which are owned by the assignee of the instant invention and are incorporated by reference herein have generally been designed to read indicia having parts of different light reflectivity, i.e., bar code symbols, particularly of the Universal Product Code (UPC) type, at a certain working range or reading distance from a handheld or stationary scanner.
A variety of mirror and motor configurations can be used to move the beam in a desired scanning pattern. For example, U.S. Pat. No. 4,251,798 discloses a rotating polygon having a planar mirror at each side, each mirror tracing a scan line across the symbol. U.S. Pat. No. 4,387,297 and No. 4,409,470 both employ a planar mirror which is repetitively and reciprocally driven in alternate circumferential directions about a drive shaft on which the mirror is mounted. U.S. Pat. No. 4,816,660 discloses a multimirror construction composed of a generally concave mirror portion and a generally planar mirror portion. The multimirror construction is repetitively reciprocally driven in alternative circumferential directions about a drive shaft on which the multimirror construction is mounted. All of the abovementioned U.S. patents are incorporated herein by reference.
In electro-optical scanners of the type discussed above, the xe2x80x9cscan enginexe2x80x9d including the laser source, the optics, the mirror structure, the drive to oscillate the mirror structure, the photodetector, and the associated signal processing and decoding circuitry all add size and weight to the scanner. In applications involving protracted use, a large heavy hand-held scanner can produce user fatigue. When use of the scanner produces fatigue or is in some other way inconvenient, the user is reluctant to operate the scanner. Any reluctance to consistently use the scanner defeats the data gathering purposes for which such bar code systems are intended. Also, a need exists for compact scanners to fit into small compact devices, such as notebooks.
Thus, an ongoing objective of bar code reader development is to miniaturize the reader as much as possible, and a need still exists to further reduce the size and weight of the scan engine and to provide a particularly convenient to use scanner. The mass of the moving components should be as low as possible to minimize the power required to produce the scanning movement.
It is also desirable to modularize the scan engine so that a particular module can be used in a variety of different scanners. A need exists, however, to develop a particularly compact, lightweight module which contains all the necessary scanner components.
It is an object of the present invention to reduce the size and weight of components used to produce scanning motion of the light beam, and to collect the reflected light.
A related object is to develop an electro-optical scanning system which is both smaller and lighter in weight.
It is yet a further object to produce a module which may be manufactured conveniently, and at low cost.
A related object is to provide a module which may be assembled easily.
Briefly, and in general terms, the present invention provides a retro-reflective scan module in an electro-optical reader operative for directing a light beam to, and for detecting light reflected from, a bar code symbol to be read. The module includes a generally planar, rectangular support such as a printed circuit board, a light source such as a laser, an optical element such as a curved collection mirror, a reciprocally oscillatable scan mirror, and a sensor such as a photodiode.
In a preferred embodiment, the laser beam from the laser passes through an aperture in the collection mirror along a first optical path to impinge on the scan mirror. Light collected by the collection mirror is directed to the sensor along a second optical path. The laser beam impinging on the scan mirror is swept along a third optical path to the symbol for reflection therefrom. The reflected light impinging on the scan mirror is directed along a fourth optical path to the collection mirror.
In accordance with the invention, the second and third paths cross, thereby resulting in a compact design in which the laser and the sensor are located away from each other at opposite end regions of the support. The compact module has the form factor of a rectangular parallelepiped having dimensions less than 20.6 mmxc3x9714.2 mmxc3x9711.4 mm.
In accordance with another feature of this invention, the laser beam emitted by the laser does not directly impinge on the scan mirror, but instead, directly impinges on a fold mirror which reflects the laser beam to the scan mirror. The fold mirror may be reciprocally oscillated in order to obtain two-dimensional scanning of the symbol, or may not be oscillated in order to obtain one-dimensional scanning. When not oscillated, the fold mirror is effectively stationary and acts as a fixed mirror. A drive for the fold mirror is selectively disabled in order not to oscillate the fold mirror.
The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. Further features of the invention are set out in the appended independent claims, and further preferred features are set out in the dependent claims.